1 Field of the invention
This invention relates to an abnormal vibration detecting device for a washing machine for detecting abnormal vibration during rotation of a dehydration tub and more particularly to such an abnormal vibration detecting device of the type that the abnormal vibration of the dehydration tub is detected based on motor speed characteristics.
2. Description of the Prior Art
In conventional automatic washing machines, a rotational tub 2 serving both as a wash tub and a dehydration tub is driven by a dehydration motor 1 also serving as a wash motor, as shown in FIG. 7. The dehydration tub 2 is sometimes rotated in an unbalanced state during the dehydrating operation. In such a case, the dehydration tub 2 abnormally vibrates during its rotation. This abnormal vibration of the dehydration tub 2 is detected so that the dehydrating operation is interrupted. More specifically, upon occurrence of rotation of the dehydration tub 2 in the unbalanced state, a water-receiving tub 3 is abnormally vibrated as well as the dehydration tub 2. A detection lever 4 is provided for detecting the abnormal vibration of the water-receiving tub 3. The dehydrating operation is interrupted by a detection switch 5 responsive to the detection lever 4. The detection lever 4 is engaged with the water-receiving tub 3 only when the dehydration tub 3 is abnormally vibrated. The abnormal vibration of the dehydration tub 2 or the water-receiving tub 3 is thus detected mechanically.
The dehydration tub 2 is vibrated not only in the transverse direction but also in the vertical or longitudinal direction during the dehydrating operation. As a result, the dehydration tub 2 is abnormally vibrated in a mode that the transverse and longitudinal vibration components are composed. The above-described abnormal vibration detecting means comprising the detection lever 4 and the detection switch 5 are mainly suitable for detecting the transverse vibration component and not suitable for the detection of the longitudinal vibration component.
The rotational speed of the dehydration tub 2 is not increased desirably even when the vibration is mainly composed of the longitudinal vibration component, and accordingly, there is a possibility that the operation of the washing machine continues without smooth progress of the dehydration.
Means has been proposed for exclusively detecting the longitudinal movement of the dehydration tub 2. However, actual vertical movement of the dehydration tub 2 does not reflect the magnitude of the longitudinal vibration. Consequently, it is difficult to detect the abnormal longitudinal vibration by the method that the vibratory movement of the dehydration tub is mechanically converted to strokes, as is described above.